1. Field of the Invention
The present invention relates to a sheet conveyance apparatus and a recording apparatus that records an image on a sheet.
2. Description of the Related Art
In an image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2005-156974, misregistration and a misaligned posture of the tip of a long sheet are corrected by causing the long sheet to move along a bump guide in parallel along a conveyance direction by a skew roller pair whose rotation surface is tilted toward the bump guide. Twist tension generated in the long sheet is reduced by generating a loop in a loop conveyance unit provided upstream of the guide immediately before the long sheet being caused to move along the bump guide so that skew correction processing with a reduced load can be performed.
Then, image formation with less skew is realized by sandwiching the sheet between a line feed roller pair on the downstream side and restarting conveyance after the skew roller pair being detached.
However, in a configuration, such as that discussed in Japanese Patent Application Laid-Open No. 2005-156974, in which the skew roller pair is detached after the skew at the tip of a long sheet is corrected to allow the long sheet to be conveyed, an issue actually arises of deteriorating conveyance precision with the sheet skewed during conveyance. Reasons for the issue include a factor that because the skew roller pair is detached, torsional tension of the long sheet directly affects the line feed roller pair to deteriorate conveyance balance, resulting in the skew.
If the long sheet is made to be conveyed along the bump guide by the skew rollers, there is an issue that satisfactory image quality cannot be obtained due to an occurrence of surface defects of the sheet because the sheet is conveyed in a state in which the surface thereof is slidingly rubbed by the skew rollers.
Japanese Patent Application Laid-Open No. 2007-225947 discusses a printing apparatus in which a pair of regulatory guides on the left and right sides is provided on a paper path route of roll paper to prevent meandering. Meandering of the roll paper can be prevented by moving the left and right guides to pushed-in positions narrower than the width of the roll paper to correct the posture of the roll paper and then, moving the roll paper width guide position.
In an apparatus discussed in Japanese Patent Application Laid-Open No. 2007-225947, a conveyance roller is provided upstream and downstream of a paper width guide to sandwich and convey roll paper. When meandering is corrected, pressure contact of the conveyance rollers is released and an operation of pushing in roll paper edges further narrower than the paper width by a guide unit is performed. Also, the position of the guide unit is moved according to the width dimension of the roll paper input into the apparatus in advance.
However, to respond to user needs more wide-ranging than in the past, issues cited below manifest themselves when an attempt is made to obtain better printing results by conveying various media with higher precision than in the past:    (1) If meandering occurs during printing and pressure contact of a conveyance roller is released to correct the meandering by a guide unit, conveyance precision of roll paper deteriorates. If a pressure contact force of the conveyance roller is weakened to correct the meandering without releasing pressure contact, conveyance precision of roll paper also deteriorates. Thus, it is difficult to ensure both excellent conveyance precision and meandering correction performance during printing at the same time.    (2) If an operation to push in the guide unit further narrower than the paper width is performed, buckling may occur depending on rigidity of the roll paper to be used so that damage due to the buckling remains in the roll paper.    (3) While the guide unit is aligned based on the roll paper width size input in advance, a gap may arise between the guide unit and roll paper edges due to an error between the actual roll paper width and the input value, precision of parts of the guide unit, positioning precision or the like, thus increasing the possibility of an occurrence of meandering. Conversely, if the guide position swings in a direction in which the roll paper is pushed in, a phenomenon similar to (2) may occur.